1. Field of the Invention
The ability to employ naturally occurring receptors or antibodies directed to specific compounds in assaying for the presence of a compound of interest has created a burgeoning immunoassay business. In each of the assays, a homologous pair, usually an immunological pair, involving a ligand and a receptor (antiligand) is involved, wherein one of the members of the immunological pair (mip) is labeled with a label which provides a detectible signal. The immunoassay methodology results in a distribution of the signal label between signal label bound in a complex of the mips and unbound signal label. The differentiation between bound and unbound signal label can be as a result of physical separation of bound from unbound signal label or modulation of the detectible signal between bound and unbound signal label.
For the most part, immunoassays have been directed to quantitative determination of a wide variety of compounds of interest, particularly drugs, in clinical laboratories requiring relatively sophisticated equipment and careful technique. Immunoassays have found less extensive commercial application where semi-quantitative or qualitative results would be acceptable and where the determination would involve non-laboratory personnel, such as in a home or a medical practitioner's office. Even in the clinical laboratory, simple and rapid screening tests employing inexperienced personnel could sever to provide substantial economies.
In developing an immunoassay, there are many considerations. One consideration is to provide substantial differentiation between the observed signal resulting from signal label when bound as compared to unbound. Another consideration is to minimize interference from endogenous materials in the sample suspected of containing the compound of interest. A further consideration is the ease with which the observed signal can be detected and serve to differentiate between concentrations in the concentration range of interest. Other factors include the ease of preparation of the reagents, the accuracy with which samples and reagent solutions must be prepared and measured, the storage stability of the reagents, the number of steps required in the protocol, and the proficiency and accuracy with which each of the steps must be performed. Therefore, in developing an assay which can have application with untrained personnel, such as assays to be performed in the home, in forensic medicine, by medical practitioners, or the like, the observed result should be minimally affected by variations in the manner in which the protocol is carried out or provide for simple techniques for performing the various steps.
2. Description of the Prior Art
U.S. Pat. No. 4,168,146 describes an immunoassay test strip. U.S. Pat. Nos. 3,990,850 and 4,055,394 describe diagnostic test cards. A wide variety of patents and patent applications provide an extensive literature of different techniques for producing detectible signals in immunoassays. The following list is merely illustrative of some of these techniques which can find application in this invention. The following is a list of United States patents and patent applications and a general statement of the type of label involved:
U.S. Pat. Nos. 3,646,346, Radioactive Label; 3,654,090, 3,791,932 and 3,817,838, Enzyme Labels; 3,996,345, Fluorescer-Quencher Labels; 4,062,733, Radioactive Label; 4,067,959, Fluorescer or Enzyme Label; 4,104,029, Chemiluminescent Label; and 4,160,645, Non-Enzymatic Catalyst Label. See U.S. Pat. Nos. 3,966,897 for an electrophoretic technique employing an antibody zone and 4,120,945 for an RIA where labeled analyte is initially bound to a solid support through antibody. U.S. application Ser. No. 893,650, filed Apr. 5, 1978, U.S. Pat. No. 4,233,402, employs enzyme pair labels; 893,910, filed Apr. 5, 1978, U.S. Pat. No. 4,720,450, chemically induced fluorescent label; and 61,099, filed Aug. 26, 1979, U.S. Pat. No. 4,287,300, enzyme anionic charge labels.